Method for making perfluoropyruvic acid mono-hydrate



United States Patent ()ffice 3,467,702 METHOD FOR MAKING PERFLUOROPYRUVIC A'CID MONO-HYDRATE Stanley Selman, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation of application Ser. No. 553,048, May 26, 1966. This application Aug. 23, 1967, Ser. No. 662,833

Int. Cl. C07c 53/18 US. Cl. 260--539 1 Claim ABSTRACT OF THE DISCLOSURE Perfluoropyruvic acid and its mono-hydrate can be prepared by contacting and reacting hexafluoropropylene epoxide with a carbonyl compound at a temperature between 100 C. and 300 C. and treating the resultant acid fluoride or perfluoro-4-oXo-2,5dimethyl-2-fluorocarbonyl-l,3-dioxolane with water to produce perfluoropyruvic acid mono-hydrate. Perfluoropyruvic acid can be isolated by dehydrating the perfluoropyruvic acid mono-hydrate.

is prepared by contacting and reacting hexafluoropropylene epoxide with a carbonyl compound at a temperature between 100 and 300 C. The reaction is described by the following equation:

where R is a hydrocarbon radical of one to ten carbon atoms and R is hydrogen or a hydrocarbon radical of one to ten carbon atoms. Preferred carbonyl compounds are these compounds in which R and/or R are phenyl radicals, unsubstituted or substituted with substituents which do not interfere with the reaction.

The reaction between the carbonyl compound and the hexafluoropropylene epoxide is generally carried out under conditions in which as soon as the perfluoropyruvyl fluoride is formed, it is rapidly removed from the reaction system. This rapid removal is facilitated by carrying out the reaction at atmospheric pressure or below.

If the perfluoropyruvyl fluoride is not removed rapidly as it is formed, it dimerizes to the compound, perfluoro- 4 oxo 2,5 dimethyl 2 fluorocarbonyl 1,3 dioxolane, having the structure Perfluoropyruvyl fluoride can be maintained in contact with the reaction system, so as to form its dimer, by using a closed reaction vessel or by condensing and returning the volatilized perfluoropyruvyl fluoride back into the reaction vessel.

Patented Sept. 16, 1969 Both perfluoropyruvyl fluoride and its dimer are hydrolyzed by water to perfluoropyruvic acid releasing hydrogen fluoride, the perfluoropyruvic acid being obtained in the form of its mono-hydrate II CFa-O-C O OH-HzO The acid mono-hydrate can be converted to the anhydrous acid by the use of conventional dehydrating agents such as H2804 01 P205.

The resulting acid or its mono-hydrate may be reacted with bases, alcohols, and similar reagents to give acid derivatives normally obtained with fluorocarbon acids.

Reaction of perfluoropyruvyl fluoride with hexaflu0ropropylene epoxide in an inert aprotic organic solvent, preferably aliphatic polyethers having from 4 to 10 carbon atoms or aliphatic nitriles having from 2 to 4 carbon atoms, in the presence of an alkali metal fluoride catalyst, such as NaF, RbF, or CsF, results in the formation if the temperature is maintained below C., and preferably between l0 and 50 C. At these temperatures, if the epoxide is omitted from the reaction system, the dimer of perfluoropyruvyl fluoride is formed. The dioxolane, perfluoro 2,4 dimethyl 2 fluorocarbonyll,3-dioxolane, having the structure (IJF --(IJFCF 0\ /0 FOO-C-CF;

is prepared by rearrangement of the dioxane. This rearrangement can be carried out in the presence of an inert aprotic organic solvent and alkali metal fluoride catalyst at temperatures in excess of C. Thus, the temperature of the dioxane reaction system need only be raised after the in situ formation of the dioxane in order to make the dioxolane.

Although perfluoropyruvic acid is an extremely potent insecticide, the perfluoropyruvyl fluoride and its cyclic dimer are relatively inert. Hence, these two compositions are useful as soil fumigants and insecticides. In addition to forming perfluoropyruvic acid, these compounds also release hydrogen fluoride, which is an effective insecticide itself, when contacted with moisture.

The cyclic oxygen containing ring compounds formed from perfluoropyruvyl fluoride are useful intermediates in the formation of oxygen containing fluorocarbon solvents which are temperature stable and chemically inert and yet have good solvent properties, characteristic of cyclic ethers. The solvents are formed from the abovedescribed cyclic intermediates by reaction with sulfur tetrafluoride which converts the carbonyl groups of the cyclic compounds to CF -groups. Thus, the cyclic intermediates can be converted to the following fluorocarbon ether solvents:

All of the described cyclic derivatives of perfluoropyruvyl fluoride and perfluoropyruvyl fluoride itself react with aqueous ammonia to result in ammonium salts which significantly lower the surface tension of water and, thus, are of utility as dispersing agents.

The invention is further illustrated by the following examples.

EXAMPLE I Into a 500 ml. three necked flask, containing a gas inlet tube, a mechanical stirrer and a gas outlet tube is placed 200 g. of benzophenone. The gas outlet tube is connected to two cold traps in series. The first trap is maintained at C. and the second trap at 80 C. during the reaction. The reaction flask is heated to, and maintained at, 225 C., while hexafluoropropylene epoxide is passed through the vigorously stirred benzophenone at 80 ml. per minute for five hours and then stopped. The reaction is carried out at atmospheric pressure.

The combined reaction product from both traps weighs 150 g. This proudct consists of a small amount of trifluoroacetyl fluoride, about 30 g. of unreacted hexafluoropropylene epoxide and a remainder consisting of perfluoropyruvyl fluoride. The perfluoropyruvyl fluoride is purified by fraction distillation through a two foot, glass-helixpacked, low temperature column.

Perfluoropyruvyl fluoride is a yellow liquid which has a boiling point at +9 to +10 C. and characteristic infrared absorption bands at 5.4 and 5.6 microns. Nuclear magnetic resonance has further confirmed the structure of the product obtained. Hydrolysis of the perfluoropyruvyl fluoride by passing through water at room temperature, results in the formation of perfluoropyruvic acid hydrate having a melting point at 122 to 125 C.

Calculated for 22.5% C; 35.6% F. Found: 22.1% C; 34.4% F. Neutralization equivalentCal.: 160. Found: 158.

The perfluoropyruvyl fluoride is converted into the sodium salt by passing through aqueous sodium hydroxide. Perfluoropyruvyl amide is formed by reacting the fluoride with ammonia; reaction with aqueous ammonia results in the formation of the ammonium salt of the acid.

Perfluoropyruvyl fluoride is also formed when benzaldehyde is substituted for benzophenone in the abovedescribed procedure.

EXAMPLE II Into a 330 cc. stainless steel lined autoclave is placed 150 g. of benzophenone and 137 g. of hexafluoropropylene epoxide. The autoclave is heated at 185 C. for 4 hours with agitation under autogenous pressure, cooled to room temperature and the volatiles are vented. The liquid reaction product consists of two layers, which are separated. The low boilers dissolved in the upper layer are distilled out in vacuo and condensed in a cold trap (78 C.). They are combined with the lower layer and the total product is distilled through a 3 Podbielniak column. There is obtained 77 g. (67%) of perfiuoro-4-oxo- 2,5-dimethyl-Z-fluorocarbonyl-1,3-dioxolane, B.P. 72 C., having the structure Calculated for C F O 25.0% C; 52.7% F. Found: 25.4% C; 51.8% F.

Infrared and nuclear magnetic resonance spectra are in accord with the structure of the compound.

Use of benzaldehyde instead of benzophenone results in the formation of the same compound in lower yield.

Hydrolysis of the dioxolane by mixing with water results in perfluoropyruvic acid mono-hydrate which is dehydrated by dissolving the mono-hydrate in concentrated H 50 heating the resultant solution to 80 C. for 1 hour,

and recovering the anhydrous acid from the solution as a distillate by vacuum distillation.

EXAMPLE III Into a 200 ml. flask containing a magnetic stirrer is placed 3 g. of cesium fluoride and 20 ml. of the dimethyl ether of diethylene glycol. The flask is cooled to 0 C. and 44 g. of perfluoropyruvyl fluoride is added. A small portion of the contents of the flask is withdrawn, distilled, and the dimer of perfluoropyruvyl fluoride, which is identical with the compound prepared in Example II, is obtained. The reaction mixture is kept at 0 C. and hexafluoropropylene epoxide, 50.6 g. is gradually added. The reaction proceeds rapidly during the addition of the epoxide consuming the epoxide as rapidly as it is added. The lower layer of the total reaction product is separated and distilled through a 3 Podbielniak column. There is obtained 57 g. (73%) of perfluoro-2-oxo-3,6-dimethyl- 1,4-dioxane, B.P. 70.0-70.5 C.

Calculated for C F O 23.2% C; 61.3% F. Found: 23.5% C; 60.6% F.

Infrared and nuclear magnetic resonance spectra are in accord with the structure.

Perfluoro-2-oxo-3,6-dimethyl-1,4-dioxane is also obtained when perfluoro-4-oxo-2,S-dimethyl 2 fluorocarbonyl-1,3-dioxolane is used in place of perfluoropyruvyl fluoride.

Perfluoro-2-oxo-3,6-dimethyl-1,4-dioxane is added to water and hydrolyzed over a period of 8 hours. The resulting product is perfluoro-2-methyl-3-oxa-5-oxo-hexanoic acid hydrate. This hydroxy acid is neutralized by addition of aqueous sodium hydroxide and converted to the corresponding keto acid, perfluoro-2-methyl-3-oxa-5- oxo-hexanoic acid, by reaction with concentrated sulfuric acid.

Calculated for C F O H: 23.4% C; 55.5% F. Found: 23.3% C; 55.4% F.

The keto acid, B.P. 50 C. C/1 mm. Hg, is extremely hygroscopic forming a solid hydrate when exposed to the atmosphere. Both the keto acid and its hydrate are outstanding dispersing agents causing a significant lowering of the surface tension of water.

EXAMPLE IV The reaction mixture of Example III obtained on reaction of perfluoropyruvyl fluoride with hexafluoropropylene epoxide is heated for 5 hours in a steel lined autoclave at a temperature of C. The lower layer of the resulting product is distilled and yields perfluoro-2,4-dimethyl-2-fluorocarbonyl-1,3-dioxolane, B.P. 60.5 C. in 70% yield having the structure Calculated for C F O 23.2% C; 61.3% F. Found: 23.2% C; 61.3% F.

Infrared and nuclear magnetic resonance spectra are in accord with the structure of the compound.

The dioxolane is converted to a fluorocarbon solvent by reaction with sulfur tetrafluoride at a temperature of to 200 C. in a pressure autoclave using hydrogen fluoride as the catalyst to give a compound having the structure As many apparently widely different embodiments of this invention may be made without departing from the 5 6 spirit and scope thereof, it is to be understood that this OTHER REFERENCES invention is not limited to the specific embodiments there- McBee et l J f Am. Chem. 806., v PP- 3152 of except as defined 1n the appended claim. 3153 (1953) What is claimed is: Garino et aL, Gazzette Chimica Italiano, vol. 60, pp. 1. A process for making perfiuoropyruvic acid mono- 5 582592 (1930). hydrate comprising contacting and reacting perfiuoro-4- Hudlicky, Chemistry of Organic Fluorine Compounds, 0X0-2,S-dimethyl-Z-fluorocarbonyl-1,3-dioxolane with Wa- The Macmillan Co., pp. 205-207 (1962). ter and obtaining as a result thereof said acid mono- Knunyants: Chem. Ab., vol. 51: 11,234(g) (1957). hydrate. Lovelace et a1.: Aliphatic Fluorine Compounds, p. 3

References Cited 10 (1958) Reinhold Publishing Corporation, New York.

UNITED STATES PATENTS LORRAINE A. WEINBERGER, Primary Examiner 2,396,076 3/ 1946 Refining ell A. P. HALLUIN, Assistant Examiner 

